The destructive capability of explosive munitions is intended to be directed against an aggressor. However, this same lethal and/or damaging potential can result in the loss of manpower and capability of our own forces in the event that the munitions is mishandled, subject to fuel fire and/or cook-off conditions, or projectile and/or shock scenarios. Furthermore, the propagation of the damaging reaction from the initiating munitions to adjacent material and munitions can greatly enhance the severity of damage.
Various munitions motor cases provided with fire exposure safety features are known in the patented prior art.
U.S. Pat. No. 3,665,857 discloses a rocket motor case provided with a safety ejection plug which is sealed to the case by a sealant having a melting temperature lower than that of the auto-ignition temperature of the encased projectile charge, to enable the plug to be ejected from the case for pressure release when exposed to dangerously high temperature.
U.S. Pat. No. 4,494,373 discloses a rocket motor case having a cook-off safety feature, wherein selected portions of the case are structurally strengthened and thermally protected while other selected stress points in the case are left unprotected, thereby causing the case to rupture at the unprotected points for pressure venting if the case is exposed to abnormally high temperatures.
U.S. Pat. No. 5,170,007 discloses a roll-bonded, insensitive munitions motor case and method of production. The motor case comprises a sheet of fiber reinforced thermoplastic, thermoset or other suitable material rolled to form a case with a tubular configuration having at least one layer of material, and a coating of adhesive on at least part of the sheet for bonding the sheet to itself for maintaining the tubular configuration. The adhesive has a bond-strength breakdown temperature which is below the auto-ignition temperature of the housed propellant, thereby enabling the case to separate and un-roll when the breakdown temperature is reached to preclude dangerous propellant pressurization within the case. The method of production includes the steps of applying an adhesive to the sheet, rolling the sheet around a cylindrical tool to form a tubular case having at least one layer, and curing the case. Preferably the case is cured while on a tool which has a coefficient of thermal expansion which is greater than that of the sheet to ease removal of the case upon cooling. The casing sheet may be rolled such that there is a longitudinal section which has one less layer of material than the remainder of the case, whereby the case would fail along that longitudinal section if over-pressurization should occur.
U.S. Pat. No. 5,976,293 discloses a dimensionally stable Insensitive Munitions case for supporting and controllably combusting propellant and/or gas-generating combustion gases. The case is permeable to the combustion gases produced at temperatures above ambient temperature but below the auto-ignition temperature of the propellant and/or gas-generating supported therein. The case is dimensionally stable without the use of metals, alloys or the like that yield shrapnel upon explosion in the barrel section of the case.
U.S. Pat. No. 6,038,979 describes a process and material for forming a warhead casing. The material consists of tightly wound carbon fiber bonded by a room temperature curing resin. The process eases and speeds manufacturing and eliminates the need to do inside threading as the interior of the casing can be totally formed during winding of the carbon thread.
U.S. Pat. No. 6,386,110 provides a deforming charge assembly which has co-axially arranged inner and outer cylinders formed from carbon fiber. Each cylinder has a first layer of circumferentially wound carbon fiber, a second layer of unidirectional carbon fiber sheet and a plurality of layers of carbon fibers circumferentially wrapped around the second layer. Detonation barrier members are disposed between the inner and outer cylinders and bolted to the cylinders on the wrapping machine.
While the prior art motor cases enable some protection against dangerous propellant pressurization, they can be difficult and expensive to manufacture, and often do not provide adequate venting to insure safe release of the propellant energy.
Therefore, a need has been created for an economical, reliable and tailorable munitions case which provides the necessary structural integrity under normal conditions essential to its primary mission, while allowing structural degradation when the case reaches a predetermined, abnormal elevated temperature which is below the auto-ignition temperature of the encased propellant, thereby precluding dangerous propellant pressurization within the case. The motor case and method of production of the present invention meet this need.